1. Field of the Invention
The invention relates to a composite optical film including a structuralized substrate, and in particular, to an optical film capable of enhancing brightness, automatically diffusing light and blocking defects, and further in particular, to a composite optical film applicable to a flat panel display.
2. Description of Related Art
Flat panel displays are widely used for television displays, computer displays, and the displays of hand-held electronic apparatuses (e.g. mobile phones, mobile internet devices (MID) and so on). Liquid crystal displays (LCDs) pertain to a kind of the flat panel displays. LCDs display images by using a liquid crystal module having a pixel array.
FIG. 1 illustrates a conventional LCD. A backlight LCD 10 comprises a liquid crystal display module 12 and a backlight module 14 forming a plane light source. The backlight LCD 10 further comprises several optical films such as an upper light diffusion sheet 22, a lower light diffusion sheet 24 and brightness enactment sheets (26, 28) interposing between the liquid crystal display module 12 and the backlight module 14. The liquid crystal display 12 comprises liquid crystals sandwiched between two transparent substrates and a control circuit for defining a two-dimensional pixel array. The backlight module 14 has a plane light distribution and serves as a backlight directing light on a plane. As shown in FIG. 1, an edge-type backlight has a linear light source 16 disposed along an edge of a light guide plate 18. A reflecting sheet 20 is used to direct light from the linear light source 16 into the light guide plate 18 so that the light passes the uppermost surface of the liquid crystal display module 12. The optical films of the upper diffusion sheet 22, the lower diffusion sheet 24 and the brightness enactment sheets (26, 28) can redistribute or concentrate the through light. Thus, the light leaving from the optical films can be directed so that it goes towards a direction quite close to the normal line of the surface of the liquid crystal display module 12. The light is evenly distributed on the plane surface of the liquid crystal display module 12 and has a relatively high intensity along the normal line direction.
Power saving, less thickness and lightness is increasingly in demand for the liquid crystal display under constant quality. Therefore, the power dissipation, weight and thickness of the backlight module would be expectably reduced, and the thicknesses of the optical films therein would be also accordingly reduced. Most conventional liquid crystal displays have used two brightness enhancement sheets (as shown in the LCD of FIG. 1). Two brightness enhancement sheets are arranged by rotating them around the normal lines of the film planes so that the longitudinal directions of grooves on the two films are perpendicular to each other. Therefore, the light through the two films would be concentrated along the direction perpendicular to their light output surfaces. When optical turbulence occur in one of the flat surfaces or structuralized surfaces of the two brightness enhancement sheets, a displayed image consequently has undesired visual effects such as interference fringes (i.e. patterns having interlaced bright and dark stripes). The undesired visual effects resulting from the interference fringes, physical defects, spots and unequal distribution can be masked by an upper diffusion sheet 22 (e.g. the upper light diffusion sheet 22 above the brightness enhancement sheet 26).
Up to now, in order to reduce the entire thickness of all optical films in a liquid crystal display, a lot of technologies have focused on reducing the number of optical films used therein. For example, four optical films (FIG. 1 illustrating the optical films 22, 24, 26 and 28) are reduced to three optical films. For a common case, the upper light diffusion sheet 22 and the brightness enhancement sheet 26 are integrated into a single composite optical film, and the single composite optical film is further combined with the lower light diffusion sheet 24 and the brightness enhancement sheet 28 into a three-sheet structure. A liquid crystal display using such a three-sheet structure is widely employed in hand-held electronic apparatuses and laptop computers.
Further, in order to reduce the dimension and the cost of such products, the display manufacturers still need a liquid crystal display with a lighter and cost-effective optical structure superior to one with a three-sheet structure. Such an optical structure is capable of enhancing brightness, automatically diffusing light and masking defects.